3 specific phones not registerd to PBX

[Eyalf83]

Hello guys,

I have an issue which I cannot overcome;

I'm using a PBX which located over the internet.
all phones are registered and working good except 3 phones - which getting timeout while trying to register.
I have seen that all phones are outbound with a random ports and registered to the PBX with random ports except those 3 phones who are outbound with port 5060 and trying to register with port 5060. so I guessing this is the reason they are timeout because all of them trying to register with the same port.

I have checked everything on the phone settings and I couldn't find a thing.

There is an option to force those phones to outbound with random ports?
I know it supposed to be by default.

Thanks