Hi. Could you try to answer the follwing questions please?
Is he bright and happy?
Is he eating normally?
How old is he?
Is he gagging as if he wants to be sick?
Has he been sick recently?
Here are the things that come to mind regarding his loss of voice:
This is most likely to be inflammation around his larynx/pharynx (laryngitis/pharyngitis).This could simply be an infection - just like you or i getting a sore throat. This is likely to improve, although may need a course of antibiotics and antiinflammatories from your vet if it continues.
There is a possibility of something being stuck in his throat, although the fact that he is eating suggests this is unlikely. they tend to gag constantly and sometimes salivate a lot.
If he has previously vomited, then sometimes this can 'scald' the back of the throat and lead to pharyngitis.
I think if he is eating well, then a pharyngitis is most likely, so hopefully things should improve. The usual applies though - if he is unwell in himself, or if it continues, you should see your vet.
I hope this helps. Do let me know how he gets on.