DIAGNOSIS The Phomemo app is likely overloaded with cached data or is out of date, causing it to crash when accessing the more memory-intensive features like the icon library.
FIX First, force-close the app on your phone. Then, clear its cache. On an Android, go to Settings > Apps > Phomemo > Storage > Clear Cache. On an iPhone, offload the app (Settings > General > iPhone Storage > Phomemo > Offload App) and then reinstall it. After clearing cache or reinstalling, reopen the app and let it re-sync with the label maker. Try the fonts/icons again.
IF THAT DIDN'T WORK Make sure your phone's operating system is reasonably up to date. An old iOS or Android version can struggle with newer app requirements. Also, check the app store for an update to the Phomemo app itself—they issue patches for stability.
HEADS UP The D30 stores fonts and templates internally, but the app handles the previews. If you have an older or lower-memory phone, try creating your label with just text first, save it, and then go back to edit and add one icon at a time. Don't overload the design canvas.