Is it okay/common/good to mention the submitted papers in my phd thesis? I have a couple of papers that I have submitted to some journals but no feedback is received yet. meanwhile i'm writing my phd thesis and the defense is in few months, surely before getting any feedback from the journals. I'm wondering if it is okay to mention those submitted journal papers in my thesis.
Yes. It is both OK and common to mention them as Articles Submitted, or as Manuscripts Under Review, or in case you have any (e.g. arXiv) preprint, Article Preprints (with the appropriate arXiv identifier). 

It might be relevant for me to point out from personal experience, that the only instruction from my department in this regard was - "Everything mentioned in the list of publications in the thesis has to be either published, or submitted for publication. There shouldn't be anything in the articles to be submitted category, because that category could be inflated as much as a person desires". The last part may be field and institute-dependent, but I think this conveys the basic ideology. Articles submitted are safe in terms of inclusion.