Video/voice calls aren't part of our processes. We do all our communication via our dashboard or email to make sure everything gets logged in our system.   This way, other designers, your project manager and the QA team can have access to the requests and the whole conversation in case they need to help - or when your designer goes on holiday, for instance.   It's also handy to have everything in one place in case your designer needs to check previous design requests and to make sure there's no miscommunication.   Many of our clients record a 3-5 minute video/screencast explaining their requests as they find it easier. Other ways of sending design requests are using bullet-points or annotated images.