Apple series 3 watch and MFP

I’m thinking of coming away from Fitbit to an Apple 3 watch. I can’t wear my watch at work but am very active there. Can I use my iPhone to count steps and then sync this data with data from my watch which I’d wear for the remainder of the day and at the gym to get a total calorie count, steps etc for the day to sync with MFP. If I can would I need other apps etc. Thanks for any advice