Is there a non-romantic phrase for missing someone?

• Your absence has resulted in a sense of loss. (Pretty impersonal and somewhat morbid. I can picture this being said by some distant relative at a funeral.)
• It would be nice if you were here. (Flirtatious.)
• I miss your friendship. (Suggests that they used to be friends, but no longer are.)

How about:

• I miss hanging out together.
• It's boring here without you.
• Things aren't the same when you're not around.
• When are you coming to visit me?

The answer is highly subjective depending on how close the friendship is, the type of humor, how well 'they' know each other. What I mean by that is if they are very close and have a slightly naughty side they can get away with sexual connotations because they know their friendship will never go that way nor do they want it to (or at least one of them doesn't).

• I miss sleeping with you! (As in spending the night together for some reason, but not sex.)
• Did you replace me yet? (As in, did they find a new friend while you've been gone.)
• Remember the times when we'd... (Good for reminiscing.)
• I miss your ugly mug. (Old style for: I miss your face.)

I miss you chum or pal -both unromantic

• Stop being a stranger.
• Where've you been?!
• When you around again?
• Not seen you in ages.
• When you next free? We need a catchup.

Just be informal.

I think this is a very valid question, and it is hard to say you like someone without a hint of romance.

Maybe: "It is good to see you again!" (with a smile) if they are around for a moment.

or: "I enjoy your company. I wish you were around more often."