What topics in user experience can have areas to do PhD in?
Yes. (My Ph.D., for example, relates strongly to UX, although it is in cognitive science / computer science.)
There are a lot of ways to come at UX. Pick one that interests you, and start looking at professors who are doing work in that area. Look at papers they are writing and research they are leading.
Read conference proceedings and figure out who is leading the research behind papers that look interesting. Read CHI and CSCW and HCI and IUI and UPA and UXE. See a name on more than one paper that fascinates you? Send them an email and see whether they're looking for new students.
You're not going to figure out your Ph.D. topic in the first year. So pick professors that seem like they are interested in general areas you can work within, and expect to rattle around a bit.
There are many UX topics you can do a PhD in. For a start, look at universities having a graduate program in human computer interaction (or human-machine interaction / human media interaction) and take a look at the types of research they do. Read a couple of scientific papers, and investigate the topics which people are talking about at the scientific conferences.
Some of current UX research is close to psychology (or linguistics, or anthropology, it's quite a broad subject), other topics are more focused on methodology (including statistics) or technology. If you want to to a PhD yourself, choose a topic that you're genuinely interested in and want to spend a few years of your life on.
I am doing a PhD in HCI - in the area of software use for work environments. I would suggest that you find a university that has a good HCI-type department, and talk to them about the right subject within their and your experience. It is, IMO, more important to find the right place to study and work out a topic within this to look at.
There are different research areas where UX community has strong presence. The most common is Human Computer Interaction. Furthermore, I have experienced that Pervasive Computing and Mobile Computing area are also prone to consider UX-related research.
For example, if you take a look at journals such as IEEE Pervasive Computing, you will find technical articles regarding sensors, and application frameworks but also many articles related to UX design. So you can target one of those communities depending on the specifics of your thesis, and following a UX approach will be a plus.
A good start certanly to look at a conference proceedings (especially CHI, here are this year's proceedings: http://portal.acm.org/citation.cfm?id=1979742&picked=prox&CFID=30641377&CFTOKEN=93259723 and Table of Contents). With this you can get a picture about current goings on the field.
You can also search for HCI educational programs and look for resarch topics there. A great resource for this is the HCI Bibliography website's Education section: http://hcibib.org/education/.
Finally you can ask fellow PhD students about their programs and topic. I attend a Computer Science PhD school and my research topic is usability and processes.
People come to the ux from a lots of fields, engineering, programmings, designing etc, To understand people before designing. how people read, write, mental process. You should look at Psychology of User experiences and UX/HCI.