I am doing a phenomenographic study on the reading experiences of avid v. Neutral v. Non-Readers. If I use a likert survey to criterion sample for participants, does that make it a mixed method study or is it still qualitative?
Qualitative vs. mixed methods depends on the type of data you are collecting and analysis for your research. Likert survey is used to quantify data about opinions or attitudes. As a result the data collected is quantitative in nature. It could be mixed if the survey asks open ended questions and participants are allowed to create text.
Being quantitative, qualitative, or mixed is of course related to the type of data and to the instruments to acquire them. However, it is also related (more importantly, I would say) to the general design of your research; i.e., to how you plan to use the results arising from your different sources of information and how you plan to integrate them in case you use more than one.