This will not be legal in most countries.
The telephone signalling is classified as TNV (-1, -2 or -3) according to international standard IEC 60950. And your network is classified as SELV.
The two systems must be separated by double insulation or reinforced insulation.
Running the two systems inside a single cable sheath would mean there is only single insulation between each system (a single layer).
Don't do this. The effect on electrical safety of the telephone system as well as your network COULD be compromised, and if a fault were to find its way from one system to another and people got hurt the consequences to you would be very unpleasant.
You should have telephone and data cabling done by a licensed operator who knows the installation rules.