Stačí shromáždit data z nativního formuláře a poté použít NSURLRequest / NSURLConnection k odeslání dat na stránku vašeho php serveru.
//Example form with one php variable only. Use get URL argument notation to add more args.
NSString *rawStr = [NSString stringWithFormat:@"var=%@",textBox.text];
NSData *data = [rawStr dataUsingEncoding:NSUTF8StringEncoding];
NSURL *url = [NSURL URLWithString:@"http://myurl.com/script.php"];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
[request setHTTPMethod:@"POST"];
[request setHTTPBody:data];
NSURLResponse *response;
NSError *err;
NSData *responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&err];
NSLog(@"responseData: %@", responseData);