When shooting video, you always want the camera to be at eye height or a bit higher. That can be tricky if you’re using an iPhone or Surface without a special mount or tripod. My favorite way to get the right angle and height is to use some books (for the right height) and some canned foods (to hold the phone at the proper angle.)
Once at the right height, the phone will need to tilt forward slightly so that you don’t have a huge amount of space above your head. The cans hold the phone in place at this angle.
If you are shooting vertical video (for IGTV or Facebook) then you need a smaller can in the front so as not to block the lens.
If you are using a Microsoft Surface, then you’ll need a taller can or bottle up front. Try a 2 liter soda bottle or a bottle of wine.
If you have time to do a little shopping in advance of your shoot, I recommend getting a tripod or a device like this one to make setting up your phone easy.