[fə.zɔ̃] is the usual pronunciation in France. Faire has a highly irregular pronunciation. The letters ai are pronounced /ə/ in:

• the nous form of the present indicative.
• all the forms in the imperfect indicative.

In this other answer @Gilles explains that this strange pronunciation might have its origin in the fact that in the 17th century, the people in Paris wrongly pronounced the present participle [fə.zɑ̃] and this pronunciation spread to those other forms, and outside Paris.

I gather in France the vast majority of people will pronounce [fə] and not [fœ]. I could not say about other French speaking countries.

I wanted to refer you to an online pronunciation of the verb and hit upon this one which sounds entirely wrong to me. If you listen to the one on Wiktionary you will get it right.