This is a reply I gave 2 years ago to the same question: Being English, I would dress as if going for a job interview, as first impressions count. Shirts - Trousers and Shoes. You have not said if this is for yourself or a lady whichever way, the same applies.
i was there two years ago, dressed as kingcole advised, but there was a young fella in the entrance queue wearing shorts, t-shirt and slippers and the guard never blinked an eye...
Ol Kingcole is a merry old soul. I appreciate his advice but as a retiree no more job interviews so I will compromise and wear a nice polo and shorts. I haven't worn dress pants since my wedding 7 years ago. I'll ask my wife to wear something sexy so he doesn't even look like me. If the set up is the same as it was 6 years ago there is a window you talk through so I doubt he can see below my belt unless.....
Went to Cebu US Consulate about 7:50, number 6 in line, out before 8:30. (Wife did a great job having all required documents described on web site). Wore shorts and polo shirt. Consulate General friendly.
I went in sept in nice shorts / sport shirt. No problem. Door is nondescript door in side, thru lobby, down stairs to left, out the door, left down the side.