1 ）我要打电话给我朋友=我要给我朋友打电话=I 'd like to make a phone call to my friend.
2 ）We seldomly say我想给我朋友一个电话. Without打and给，it could be ambiguous and weird, and probably means to buy a phone for a friend not to give him a call. 给means "to someone or something".打means "to dial". You can also say 我想给我朋友来个电话 which is common in speaking.