I misunderstood at first attempt.
Then please share your misunderstanding with us, you are certainly not the only layman here and could basically explain to the other laymen in layman's terms what was misunderstood at first attempt.
Depending on what the electrician understands by the telephone connection mentioned in the construction description, it will be omitted.
Let him do what he always does, just with three tiny differences: 0. in the connection room he lets the cables start freely instead of laying them onto a VVDo # 1. he installs different cables in basically the same way otherwise (for double sockets, two) # 2. he can omit the socket inserts. To give you an idea of the smallness of the change: a 25 m reel of "telephone cable" costs 8.60 EUR, the same length of "network cable" 10.50 EUR. An unshielded "ISDN" western socket costs the same with the TAE NFN, but you take shielded network sockets "RJ45" 8P8C. The electrician only has to install the cables firstly in star topology (i.e., coming individually to each socket from the connection room, not switching the sockets as a bus or such) and secondly continuously (i.e., not patched somewhere). Whether the cable is called "Category 7", "6" or even "5" is secondary.