Can an RJ45 connector be plugged into a phone socket?

First, thank you for responding quickly as I am stuck in my momentum.
Yesterday I brought a phone socket into the wall behind my hi-fi unit where my Numericable box is located.
This socket is powered by an RJ45 cable going into a cabinet for ADSL connection (connected to the phone line for years).
In short, it's connected to a classic ADSL phone socket (like France Telecom via a general filter via a splitter via an RJ45 cable on the latter).
One additional idea, is it possible to split from this splitter using an RJ45 cable to directly connect my PC upstairs knowing that the phone would be taken from my phone socket in the wall and my PC through the RJ45 line?

If the cable is used for the ADSL connection from the box to the telephone line, it can only be used for that.

To distribute Ethernet, a network must be set up for it, with, as mentioned above, a box with RJ45 sockets for distribution to the rooms. (What is your splitter?)

Even additional telephone sockets cannot be used for the phone since the telephone output is on the box (in the case of unbundling without a France Télécom telephone subscription aside)

A foreigner is a friend we haven't met yet.

Thank you again,
I see that I'm not very good at my explanations and I will try to improve a bit.
My wish, but is it possible?
My box is powered by a Numericable coaxial cable, from which I would like to connect to a standard wall telephone socket (very important RJ45 cable) using a modular telephone socket that accepts an RJ11 cord and then another modular socket that accepts an RJ45 cord, knowing that these two cords will be connected, of course, to the corresponding sockets of the Numericable box.

The RJ45 cable arrives in my garage on a standard junction box that looks like a telephone socket (with numbered screws) from which I plan to branch out in RJ45 to supply the upstairs.

Once again, thank you

Sincerely

Indeed, we were missing a crucial piece of information regarding the issue, the ADSL by cable (edit: upon rereading the question, I realize I missed the information).

So you have a T socket where you want to connect 2 phone sockets with RJ11 and RJ45. I don't see how that could work. I wouldn't even try (and I've tried plenty of weird connections).

With this solution, you should be able to connect a phone. But not Ethernet.

For me, in this context, the solution would be to replace the T socket with an RJ45 socket, and at the other end of the cable, in your splitter, put another female RJ45 socket and for the other room, put an RJ45 outlet that you would connect to the socket coming from the box. You would thus have an Ethernet connection.

For the phone, with the boxes, the best solution is to connect a DECT phone at the box's output and have additional cordless phones in the house.

A stranger is a friend that we haven't met yet.

OK, I agree, my setup seemed a bit unorthodox.

So I decided this evening to install two wall sockets, one RJ45 and one telephone.

For the first one, whose cable arrives in my garage, I will install an RJ45 socket that I will crimp with the help of a special tool that I will buy.
It will be powered by an RJ45 cable coming from the box to the wall socket located behind my HI-FI unit where my BOX is.

I will also buy a splitter, apparently called a hub (I learned this today), which will be powered by my cable and will allow me to branch out to two or three lines on the upper floor.

For the telephone line, it’s simpler; I will run a direct line to the upper floor to my DECT answering machine, which will be powered in the same way as the RJ45 but with an RJ11.

To be honest, I have this issue of not wanting to see any wires lying around in the house, and when I did all my work, I forgot to plan for these two sockets, only in part.
Why only in part? Simply because I didn't feel the need as I was operating on the upper floor with a NETGEAR modem and the (master) phone on my desk. Fortunately, I still had a 50 conduit partially available to add wires and judiciously bring them back out in the living room by making holes with a hole saw.

I think I understood your message, and if I didn't, please let me know. In any case, I thank you for your kindness and patience. Perhaps we will meet again later for another topic.
This is my first experience in asking for help.
I am happy with the result; there are still nice people online (witty humor as (SIRET) is my name).

Sincerely

I think you're on the right track. Good idea with the distributor if you want to connect multiple rooms (the hub is a device that is becoming obsolete, you need an Ethernet switch).

I'm going to nitpick a bit ;-) The real logic in the central box is to put not a male RJ45 connector at the end of the cables, but a female RJ45 socket. This could be a small metallic strip with sockets or a connector of this type: https://www.materielelectrique.com/bloc-connecteurs-rj45-cat5-pour-panneau-brassage-equipe-p-4233.html.
Then with small cables, you make a patch cord between the rooms. That's the principle of a patch panel.

There could be another reason not to use a male connector, which is the type of Ethernet cable. Generally, in walls, one tends to use single-strand cable (each wire consists of only one metallic strand). This is a fairly rigid cable, but no worries in the wall. In contrast to multi-strand Ethernet cable (each wire is made up of several small metallic strands). This is a flexible cable, the one we use to connect devices, a patch cable male/male. Male RJ45 connectors and the corresponding crimping tools are designed to be used on multi-strand cables (there are also male connectors for single-strand cables: http://www.touslescables.com/b.php?a=A8OL*pcd^83&c=Voi&h=2214 but that's not common).

A stranger is a friend you haven't met yet.

Hello,

First, you need to know how the wiring is done (or are you doing it?). Do you have a central cabinet with the telephone entry and RJ45 outputs: https://sitelec.org/cours/abati/domo/images/vdi26.png

The RJ45 sockets might just be telephone sockets; in that case, their only use is to connect the box for ADSL.

Best regards

--
A foreigner is a friend you haven't met yet.