Accessing iPhoto on NAS using iPhone

you can not

1 - the iPhoto library can not be on a NAS - it can only be on a local drive formatted Mac OS extended (journaled) connected with a fast wired connection

2 - iPhone can not access iPhoto libraries on a Mac under any conditions

with EL Captain and Photos you can use iCloud Photo Library and it will keep all connected libraries on Macs and IOS devices identical - all additions, deletions or edits made on any device will be made on all devices

LN

If you want to see the photos from an iPhoto Library on an iPhone, sync selected albums from your iPhoto Library to the iPhone using iTunes:

See this document: Keep your photos safely stored and up to date on all your devices - Apple Support

(Scroll down to the paragraph "Sync manually with iTunes").

I'd remove the iPhoto Library from the NAS. Apple requires that an iPhoto Library is on a locally mounted volume: iPhoto: Issues with FAT32-formatted drives:

"Additionally, storing the iPhoto library on a network rather than locally on your computer can also lead to poor performance or data loss."