The reason that phone call was made

I think it’s possible that with Reghabi gone, Mark insisted they call Cobel because he knows she knows something about Gemma. The last time Mark saw Cobel (S2 E2), he asks if she knows something about Gemma and they have this whole nonverbal conversation where Mark realizes Cobel definitely knows something.

Aside from Reghabi, who’s shown she can be volatile, Cobel is the only other person that has some knowledge about what’s going on with Gemma. Was it a mistake to reach out to Cobel? Probably, but it makes sense.