How do I say no?

My boyfriend and I are in a long distance relationship for the time being. He likes to fall asleep on the phone with me and have the phone next to him while we sleep. I thought that was cute and all in the beginning but I'm slowly just starting to get tired of it. I brought this up one time, recently and this made him cry. It actually upset him that bad when I told him I need some space right now and that I need to get off the phone some nights. Now I really don't know how to bring this up again because I'm just scared of dealing with that kind of reaction again! I feel like this may even be borderline manipulative. I don't know what to do. Other than this situation, we really do have a healthy relationship where I have no doubt he loves me. He can be a little clingy and this is just one of those examples.
How do I say no?
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