It is good employment practice to make adjustments if an employee cannot do the normal job because of a temporary health issue. But there is no legal obligation (the situation is a bit different in cases of pregnancy - when an employer must demonstrate very clearly it has looked at alternatives).
For 8 weeks, your employer has made alternative arrangements and it now seems to be saying 'look, this isn't a temporary situation'. It has probably reached the conclusion that there is no end date in sight for this situation. Sorry, but I don't believe there is anything more that you can do - it has made 'reasonable adjustments' to your job role for 8 weeks. Obviously, in a Call Centre the vast majority of jobs involve using the phone. Only you can judge whether there are enough non-phone-based jobs around the patch to make the case with your employer.