May a PhD be more practical than theoretical?
To be awarded a Phd, you can't just build something: there has to be some sort of novel research component. PhD's are all about asking (and answering!) questions, not just engineering solutions to a problem.

However, there is absolutely nothing wrong with creating something new as a part of your PhD, so long as it helps you answer a research question. For example:


Does this algorithm improve the speed/reliability/accuracy with which this data can be proccessed compared to existing techniques?
Does this new collaborative learning tool improve a student's ability to learn a language compared to working individually?
Does this new system for visualising a data structure affect the way in which users perceive/engage with it?


Note that these are far too broad to be used in practice, but they might give you an idea of the types of questions that can be asked.