Phone jack must have 2 or 4 wires?
Modern phone RJ-11 jacks will properly furnish talk battery on the two center pins. A second line may be furnished on the pins straddling the center two. Look on either of these 2, line placement possibilities for yours. However, if by odd chance you have a VOIP phone set, it needs 4 wires and possibly 6.
Two, in most cases, although sometimes three are used. The other pair is supposed to be for a second line, if you have one.
Our phone used red and green back in the day. I once read that yellow and black were once planned to power transformers that would give phones illumination. https://www.pcmag.com/encyclopedia/term/50559/rj-11
for it to work it needs 2 wires on the center 2 pins. 4 wires is either 2 lines, spare pair or sometimes a digital pbx system will use the outter pair as the data system. sometimes on the dsl systems they will use red and green as tip and ring for phone and then yellow and black as the dsl pair filtering it before it comes into the house.
It depends upon the country, and phone. The standard connector is 6 conductors, but only two are required for dial tone, ring, answering, receive and send. That is referred to as an RJ-11 and only two wires are used. The conductors other than the two central tip and ring conductors are in practice variously used for a second or third telephone line, a ground for selective ringers, low-voltage power for a dial light, or for anti-tinkle circuitry to prevent pulse dialing phones from sounding the bell on other extensions. Most of the cables sold are 4 or 6 conductor even though only two are typically used. In the USA, and posisbly elsewhere, if the phone is not an old rotary dial, and not a lighted keypad Princess type phone with lights powered by the phone system, and not a multi-line then all you need is two wires.
3 - Red, Black, Green for Hot, Neutral, Ground, respectively.
four to hear AND talk, only two for an answering machine ..................................