Toilets, Sinks, Showers, Tubs and Disposals - Toilet Flushing Issue

My toilet in my upstairs bathroom is having a flushing issue. It seems when the toilet is flushed water comes in but doesn't seem to go down the hole and thus overflowing on to the tile.

It does flush however if you use a bucket to pour water into the bowl... which makes me believe it's not clogged. I tried scrubing the flush ring thinking maybe not enough water pressure was going through but it seems to be a problem with suction. What else can I try?

Thanks in advance,
Rys

I think it might be clogged and you're just not pouring the water in as fast with the bucket as when you push the handle to flush.