This may be a blocked number or private number. I've never experienced that before as my screen usually says BLOCKED or PRIVATE NUMBER. Possibly a phone call from someone Long Distance?
You are correct...it looks exactly like that but unfortunately you can't expand the cell like you can with Excel unless there is a method to do this that I don't know.
Do you think that it's just a real long phone number, like some of the numbers from Europe (IE: UK)? Do you know how many numbers the number field shows before cutting off?
I would assume that the longer the phone number, the smaller the characters would become. I doubt a phone number exists so long that it would render the phone unable to display it...