What's the URL for Valve's Steam?
If you guessed none of them except for steampowered.com, congrats!
What's the URL for Americal Eagle, the clothing store?
If you guesses all of them except americaneagle.com congrats!
The threat model for phone numbers is considerably different, not least due to the link-based nature of the web and email. The URL takes on the role of both the number and the caller ID (if caller ID didn't suck) - you should be able to be confident that you're talking to who you think you're talking to.