NAT Configuration

I had installed FreePBX and configured succesfully for LAN.
I’m using a DD-wrt router with dynamic ip and a VM with FreePBX installed behind.
I would like to access to PBX with SIP from the outside but using a non-standard UDP port to avoid attacks with a Port forwarding moving the outside to 5060 in the inside.
I used to have an asterisk that worked this way.

Can you help me with the PBX configuration?

first, a question when you say “access SIP from the outside” what do you mean? are you planning to have phones outside the firewall? or this just for your sip trunks? what protocol are you using (chan sip or pjsip)

I plan to connect cell phones. I was using chan_sip with one way audio.
I tried with an IAX extension and worked fine.