Because an employer can (not necessarily should) terminate contractors for a variety of reasons, not the least of which is expressing opinions contrary to those of and potentially unprofitable to the employer.
Now I doubt Phil was actually EMPLOYED by A&E but rather the two enterprises had a contract for the filming. But even if they were actually on payroll, A person's sexual preference is a protected class. Professing someone to be a sinner does not make one a protected class.
too bad people's religious beliefs are protected or something.