When I import a file and have phpMyAdmin determine the appropriate data structure it only uses int, decimal, and varchar types. ¶

Currently, the import type-detection system can only assign these MySQL types to columns. In future, more will likely be added but for the time being you will have to edit the structure to your liking post-import. Also, you should note the fact that phpMyAdmin will use the size of the largest item in any given column as the column size for the appropriate type. If you know you will be adding larger items to that column then you should manually adjust the column sizes accordingly. This is done for the sake of efficiency.