My Iphone 4s was replaced by the Apple store today. I previously backed everything up to Icloud. I'm downloading everything from Icloud onto the new phone. The pictures seem to have stalled on number 215 for the past hour or so.

Some users have reported that turning off the phone, then turning it back on restarted a "stuck" photo download like this. (To turn it off, hold the power button until you see the Slide to Power Off slider, then slide it.)

Then you'll have to decide when you think it's hung and unlikely to restart. At that point, you'll probably have to reset it (by holding the power and home buttons at the same time until you see the Apple logo, then release) and try restoring the backup again.

The only "solution" I've seen posted on photos that fail to restore from a backup that seems to have worked for others, is the on posted by ezjules here: https://discussions.apple.com/thread/4076441?answerId=19518589022#19518589022. If you restore the backup again, you could give it a try and see if it works for you.