Unfortunately, this dialog seems to be missing from Office 365 (e.g: Excel for Web). You can, at least, still use the UNICHAR() function to get a character you know the code of, then you can copy/paste values as needed. Not entirely pretty, but at least it works.
Question - how do I insert the "Angle" symbol. It is listed under subset "mathematical operators" and says it is character code 2220. When I hold Alt and press 2220 it returns a small "1/4" fraction? When I try to insert it manually by clicking Insert then selecting the angle symbol from the list of symbols it does something crazy to the cell height. How do I simply insert the angle symbol without Excell doing something crazy to my cell ?