Don’t say something like: “What is happening, why didn’t you call me?” This would be a turn off. He owes you nothing.
So, call him and have a friendly and open chat. “How is life?”. “I had a great time the other evening”.
Keep it light and fun. This is essential.
The goal is simple: It is to build up chemistry and have a nice friendly conversation with someone.
Make sure it is the right time. Evening works better because during day time, he can at work or have other priorities. Evenings are as well more conductive for romance.
When you call, ask him first: “are you busy right now? Do I disturb you in the middle of something?”
This question makes sure that he has time and focus for you.