Have you tried the Simulate Call feature in the Site configuration to see if the cell phone numbers work properly per the Number Plan? That would be the first place to look.
Then, if that checks out fine you would need to open a case with Care to look at the Edge and other back-end logs and see what is happening.
------------------------------
George Ganahl GCP (Genesys Cloud), ICCE
Principal Technology Consultant
Genesys
------------------------------