For test automation purposes, we're currently investigating upon how we can have a fixed phone registered with a Skype for Business IP-PBX (e.g. an AudioCodes phone or a Yealink phone or...), make an outgoing call upon request.
E.g. Our test automation platform would send a request to the Skype for Business Server to tell this server to initiate an outgoing call from phone A registered with that Skype for Business Server to an external phone B. So a little bit similar as JTAPI functionality...
I.e. Would this be feasible by using UCMA 5.0?
There is no way to SIP to make a physical phone make a call.
With UCMA you are effectively a softphone, so with UCMA you can make your "softphone" make a call.
With the Lync Client API you are remote controlling the Lync Client (Skype for Business client), so with the Lync Client API you can remote control the Lync Client to make a call.
The only way I can think of to make a physical phone dial would be to use a Polycom VVX phone linked to a instance of a Lync Client using there "Better Together" application. Then you can use the Lync Client API to remote control the Lync Client which would in turn remote control the Polycom VVX phone.