Hi Anrzej,
Right question is 50% of solution. Unfortunately the question is wrong. Almost nothing is clear.
You can register your phones (clients) and you even can start or receive calls but there is an issue with audio/video? Is it correct?
In this case this problem is not related to kamailio. It is related to pbx/media server that is possibly behind kamailio. But maybe there is no any pbx behind?
Without additional configuration audio/video traffic will go end-to-end which is a problem with external clients with no public IP.
And yes, you are right about 5060/udp. But everything depends on your configuration which is not clear. Maybe you need additionaly 5060/tcp, 5061/tcp (TLS).
But ports range for media traffic depends on media server/pbx/rtp proxy configuration and nobody can answer this question but you.
I hope this tips will help you a little bit.