====sip.conf for each of the phones=====
host=dynamic
secret=6005
context=outgoing
type=peer
encryption=yes
avpf=yes
icesupport=yes
transport=ws,wss,udp
directmedia=no
disallow=all
allow=all
dtlsenable=yes
dtlsverify=fingerprint
dtlscertfile=/etc/asterisk/keys/asterisk.pem
dtlscafile=/etc/asterisk/keys/ca.crt
dtlssetup=actpass

====extensions.conf for the context group=====
[outgoing]

exten => _X.,1,Dial(SIP/${EXTEN})
;exten => _X.,n,Answer()
exten => _X.,n,Hangup()