Spoon refusal is a really common phase around this age. Babies really want to start showing their independence and feeding themselves, so finger foods are the way to go until it passes. Offer the spoon, and if he refuses, put it away without making a big deal out of it and give some finger foods instead. You can do all kinds of steamed veggie chunks, fruit chunks, and even spread purees onto sandwiches and cut it into pieces. You can also try coating fruit and veggie chunks in dry infant cereal or crushed cheerios...that can help if the slimy texture is putting him off.
Normal formula intake around that age is 20-24 oz, but that's just an average. And keep in mind that purees are mostly water, but finger foods aren't. So it may seem like he's eating a lot less when it's finger food, but it's probably a decent amount when you factor that in. Honestly, if he isn't losing weight or waking from hunger during the night, he's probably getting plenty to eat!