The Store by default shows episodes in reverse order - newest on top - though the user can change this by clicking on the column heading,
However the iTunes application shows the episodes only in reverse order. This makes sense when someone is suscribing, since each new episode appears at the top where it is most visible (particularly if there are more episodes than will show without scrolling). I don't know what the iOS app does.
There is a tag you can use to change the order - 'itunes:episode': Apple say -
<itunes:episode> An episode number.
If all your episodes have numbers and you would like them to be ordered based on them use this tag for each one.
Episode numbers are optional for <itunes:type> episodic shows, but are mandatory for serial shows.
Where episode is a non-zero integer (1, 2, 3, etc.) representing your episode number.
https://help.apple.com/itc/podcasts_connect/#/itcb54353390
There is also an 'itunes:order' tag but Apple's Help page has given up listing all tags and now omits that one.