licences are granted by the individual states, each one has different requirements.  for example california has different requirements than alaska

1. Does one have to be licensed architect to practice architecture in US?
   1. Yes and no... it depends on the state and the size/scope of the project. You can however work for an architecture office under another's license without holding one yourself.
2. Is getting a M. Arch degree a must or requirement to get the license?
   1. It depends... The US still has the old accredited 5year B.Arch degree too.
3. How about if someone have the degree in MS. Arch, or even Ph.D related to architecture? Can they be qualified to get the license to practice?
   1. PHD? please... that's an academic degree, not a professional one. Check with what ever state you want to work in. They will list what level of education is acceptable.
4. What would be other conditions? Do they have to have working or internship experience for 2 years to get the license?
   1. Two years? Are you really that daft? Internship period can last 5+ years if you're not able to meet all the minimum requirements and let's not forget the mandatory exams,
5. Please respond to these using a layman casual words, and not simply just give me a link to a website without explaining them in your own words.
   1. Too bad, do your own damn research. You'll need useful skills like this if ever you want to jump into this profession.

http://archinect.com/news/article/149991988/ncarb-opens-up-official-certification-to-much-wider-field-of-architecture-students