Wait one more day to call him.
Although it might seem like a good idea to show him you're really interested, you don't want to appear to eager, especially by calling back too soon (he might have planned to call you later in the day).
And if tomorrow, he doesn't answer, leave a message on his answering machine, something like :
Hi, it's [Name] from [Company],
I was wondering if you had any news concerning [Position], in which
I'm still very interested.
You can reach me all day today at [Phone number], please feel free to
give me a call when you get this message.
I'm looking forward to hearing from you.
Don't remind him he said he'd call you the day before, just act like you're waiting for his call but don't rush him.