fast travel back to Kronos Island and the first Fishing Spot.
If you want to access your Egg Memos, the only way is to select the fish-o-pedia option when talking to Big the Cat. There's no way to view them in your inventory or in any menu when you're not at the Fishing Spot.
What are Egg Memos used for?
The Egg Memo collectibles may seem like they have an ulterior purpose, but they are just lore and flavour. When you purchase one you can listen to it and it'll give you a little excerpt of Dr. Eggman giving his thoughts about Cyber Space. That said, if you don't want to bother getting them for yourself since they seem to have no in-game benefit, you can always just get your Sonic lore fix by listening to them on YouTube, such as in this video by Egg Emperor: