If all your notes are missing from your iPhone, and you have a lot of notes in iCloud (I have ~25), in order for those to reappear on your iPhone, your iPhone MUST be connected to WiFi.
Once all those notes reappear, and you're only adding a note here and there, they should sync fine when you're not connected to WiFi.
So bottom line, if all your notes are gone, connect to WiFi and they should reappear on your phone.
It took escalation through 4 technician levels at Apple to resolve this issue today.
UPDATE 7/10/2018:
This still doesn't work most of the time.
Apple's support page for this issues doesn't help: https://support.apple.com/en-us/ht204051
iPhone simply loses the ability to see some networks. My PC see's the network (and I'm connected to it as I type this), I'm sitting within 1 foot of my router, restarting the router doesn't help, and resetting Network Settings (Tap Settings; General; Reset; Reset Network Settings) doesn't work either. That's all they've got.
Frustrating to be out shopping, open your iNotes to view yours lists, and see iNotes haven't been updated in ages.
Note that the calendar and other apps are working just fine (they don't need the inconvenience of having to connect to the cloud to update).
Is there a better Notes app out there? Will look but please send suggestions, thanks!