What is the best way to implement an additional VoIP phone?

Question

VoIP

Good afternoon, dear ones!
We have such a situation.
A workshop, it has a Zyxel Keenetic 4g II (White IP) for Internet reception + a D-Link DVG-5402SP is connected to it and two analog phones are connected to it.
They allocated another room, but it’s far away (300-400m, i.e. pulling from this room is not an
option
) is the best way to solve the problem?
I’m a little floating in the choice of implementation, or take a simple router + ip phone, or take a good voip router (the price bites) (but will that login / password from the voip provider on which the workshop works)
Help with advice :)

Answer 1

Drag all phones to 3CX or Asterisk.

Answer 2

VoIP over Wi-Fi - not very reliable
at 300-400m, it's best to throw copper, with repeater amplifiers