The HTML messages were not optimized for small screens.
Modern mobile phones have a browse that allows you to pinch to zoom function that lets you fit the message on your screen. I don't know if you can do that in your mobile browser.
Anyway, the largest element on the page is the 468x60 banner.
You can always get a premium subscription to avoid getting messages with ads.
phpclasses.org/premium/
In the worst case you can go in the user options page switch to text format.
phpclasses.org/user_options.html