Dual citizenship means two different countries recognize you as a citizen.  If it is legal for an American to sponsor someone, then you can because you are American.  That you are also something else does not matter at all to the USA.

You need to prove legal capacity to marry regardless. If you have any prior marriage, you must prove you are divorced (except there's no divorce in Philippines). US citizen must have a suitable home in the US for their foreign fiance/spouse, and prove sufficient earnings for self + all dependents + person they sponsor. You will need current year paystubs + last 3 years of US income tax returns to prove earnings. Spouse visas typically take longer than fiance visas, and can take twice as long. Your Philippine fiance/spouse must remain in Philippines until visa approved & issued.