Printing from iPhone vs Mac?

I constantly print things wirelessly from my Mac to my Lexmark printer. However I can't seem to print anything from my iPhone which is a 4S. Anyone know why?

Without more details it is impossible to say why. Are you using the Lexmark app…

https://itunes.apple.com/...15392?mt=8

What series is your printer?
there are various apps that you could try such as print n share or printcentral, either should solve your iphone printing problem.