I do not trust mobile phone security for banking. However, both my daughters do and regard it as very convenient.
I would quite like the facility to load my phone with some money that I could "spend" - say £100 or so. That would limit my risk if I could find a risk free way of downloading it, and adding to it every now and then. (Think of the credit carried on an Oyster card). However, the security would continue to be an issue.