Telephone is currently private conversation. Need a warrant to get in (tap).

"Need" is doing a lot of work in that sentence.

This is from just a quick unrefined search:

https://techcrunch.com/2023/03/02/secret-service-ice-warrant...

https://arstechnica.com/tech-policy/2015/06/county-sheriffs-...

Why should telephone calls be exempt? What is they are talking about child porn?

In USA it's because courts and laws sorta think it should be.

If you're a suspect they get a warrant to search (tap) and seize; which is a 4th amendment thing in USA.