So a client of mine wants to have a short call with me is this against the TOS ?
You really should read the TOS. You will find the answer right there.
You find a link to the the TOS on the bottom of each page of Fiverr.com
“To protect our users’ privacy, user identities are kept anonymous. Requesting or providing Email addresses, Skype/IM usernames, telephone numbers or any other personal contact details to communicate outside of Fiverr in order to circumvent or abuse the Fiverr messaging system or Fiverr platform is not permitted.”