The great thing about phone relationships is that they can be what you want them to be.
So, for your own purposes, you can have a vague image of this man. based on his voicec, and imagine him to be the kind of guy you like. What if he was nothing like that?
i used to speak to a girl regularly as part of my job, and we got very friendly with each other. One day, i was on holiday, and she spoke to one of my colleagues, and asked what i looked like? She said i had such a sexy voice, and in her mind I resembled a tall hunky he-man film star ...
My colleague almost needed oxygen for laughing so much she couldn't breathe!
She informed my phone friend that I looked a lot more like Woody Allen than a hunk, and as my hair went, i was morphing into Paul Mckenna!
My point is - fantasy relationships are just that - and rarely turn out well when you break the fundamental premise that makes the relationship work - anonymity.
Comfort yourself that it is perfectly possioble that he would break your image of him for ever, when this physically utterly unsuitable man appears, and then starts talkking in your fantasy man's voice.
Even worse, he may not be at all attracted to you - and that would mean rejection anyway.
See this relationship for what it is - a nice safe flirtation with no responsibility, no accountability, and sadly, by its very nature - no future.
Be open to attraction to people you meet, as friends, and as potential partners, and you will find it easier to get over this relationship which trust me, is far more transitory that you think or feel at this moment.