Which ever form of communication your client prefers. There are so many ways to communicate today (face-to-face, phone, email, text, video conference, etc.) you just have to be adept at all of them and use the one your client favors.
Generally a combination works best. At the beginning of a relationship I like to meet in-person to establish trust and understand the client’s communication style which helps to avoid miscommunications. Afterwards, we tend to fall into a preferred form of communication determined by the client.