Looking in the gateway menu, I am not seeing a means to set up a connecting to a provider via TLS/SRTP.
That does not seem correct from an ASTPP perspective.
There are only four fields available in SIP Profile.
Looking at
https://freeswitch.org/confluence/display/FREESWITCH/SIP+TLS
You need to set up external profile, and more fields are required than the ASTPP SIP profile menu provides.