This is normal and when a kid hits 2 years old.
They are changing developmentally.. and their mind too.
Both my kids did that too.
It does NOT mean that they necessarily don't need naps anymore period & absolutely. They WILL still get tired and often times still do need a nap.
So... keep to your routine EVERYDAY... and gauge it. But you need to be flexible about it. Like, Perhaps make nap time a bit later... by 1/2 hour increments.
AND, have a "wind-down" period BEFORE nap. Let the child unwind. A kid needs that. For me, it takes about 1/2 hour to get my kids wound down. THEN, nap routine. I just make everything quiet....nothing noisy, I make the room(s) dark etc. My son likes to watch "Little Bear"... its a cute show that relaxes him.
Yes its a phase. The one thing to watch out for is... absolutely throwing naps out the window and completely stopping. Because at this age through 5+ years old, they still benefit by naps. My son is 3 and still naps... my daughter up until 1st grade was still napping... and she is 7 now and will still occasionally nap. I don't force them... but I have a "routine" everyday and I KNOW when my kids are tired... or they tell me they are tired and my son will sometimes even tell me "Mommy I'm going to sleep..." and he crawls into bed himself. But every afternoon is "quiet" time. My son will not last the entire day without a nap... or he gets MEGA fussy and TOO hyper. Typical signs of an OVER-tired child.
Just keep doing what you are doing... the routine is important... and one day, AFTER the PHASE is gone... he will nap. Like the aberration never happened. BUT... keep in mind that if you get lax or irregular about it... it will be very difficult to get him BACK into his usual nap routine... so, as me and the others suggest... keep to your nap & pre-nap routine...if he is in the crib talking to himself fine... my son did that too and would play with his toys. He even sang "opera" in there. But he was happy. He'd call me sometimes, just to see me. Then he'd tell me "okay Mommy bye-bye, me sleep now.." and then he'd hunker down and doze off.
So... keep consistent. Don't "give up" naps per say nor entirely... but just try and flow with it... but keeping to the routine, everyday. You don't have to b e a forceful brute about it... but just keep a routine... and if after awhile he does not fall asleep... then take him out. BUT keep quiet, no horse-playing...and tell him "we will go back to nap in a few minutes..." then do so.
At least with my kids, the both did that.
At 2 years old, is typically when all kind of sleep/nap tweaks and aberrations occur.
All the best,
Susan