can i use my iphone 5S with apple watch series 3 (GPS)

The current shipping Apple Watch Series 3 and 5 models require an iPhone 6s, SE, 7 or newer running iOS 13.  It will Not pair with the iPhone 6 or older.

An iPhone SE will work.

An iPhone 5s will not work.

If you have a used Apple Watch Series 3 that Has Not Been Upgraded to watchOS 6, then you could pair that Apple Watch to an iPhone 5s, however, used Apple Watches can be a problem, as many used sales are either stolen watches that are still locked to the original owner's account, or the original owner did not properly prepare the watch for resale

What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else

https://support.apple.com/en-us/HT208855

If the previous followed these instructions, it will be OK. But if you are going to the used market so you can pair to an iPhone 5s, the make sure you can contact the seller after the sale, and that they do not Ghost on you and abandon the seller's account once they have your money.

If the watch has watchos6 software version then you can use with an iphone se as long as it is updated to ios13,if it has watchos5 or lower then you can only use it on the iphone se.