There is no fixed count to the number of projects you need in your UX Design portfolio. It’s all about quality rather than quantity when creating a portfolio. If you are absolutely fixed on the number of projects you want to present, keep it to the minimum. Anywhere between 3-5 projects are more than sufficient. The projects can be a mix of client work and personal experiments. This balance is essential as it will help employers understand you are open to learning and trying out new problems and coming up with ideas. Each project needs to be explained properly; you can explain the steps you took to achieve the solution. Support your text with appropriate process shots and images. Do not place absolute emphasis on your awesome UI skills; a few shots of your visuals is sufficient. Employers want to know your thought process; how you solved the problem, what went through your mind, rather than which font and colours you have used.
Having a portfolio for Designers is something a criteria in recruitment for all those who wants to start a career in UX Design.This, however, is not all companies would ask for as they will have their own process to select a candidate but having a portfolio always adds value to your profile.