hi everyone!
what is the relevance of focus group interviews in Phd researches. Are FGI considered suitable enough to collect data?

It entirely depends on what is your research question and how you justify the choice of focus groups as data collection method. Focus groups are neither illegimate nor prefered methods for a PhD:) As any other data collection method.

thankyou Verdy, What do you mean by not preferred...Do you mean to say that although they are not illegitimate but at the same time they are also not preferred?!!