Don't try to tug him up and over stairs or ramps -- this will give an even worse association with something he already fears.
The best way to address this (and dogs DO get phobias of things just as we do -- especially when we are kids!) is to use rewards to make the scary thing gradually less scary and then, *rewarding* for him.
So find a set of stairs and take a handful of realy yummy treats and first just practice walking towards it, not making a big deal about it. Don;t fuss over him or give other signals that going near the stairs is supposed to be a big deal. Walk him past them at a distance and toss him some treats or feed them as you walk right past and give some approval cue, like sayng 'yesss!'.
There is probably some distance at which he starts to baulk so your first goal is to get him to walk that close without getting worried. Then start walking towards the stairs and have a treat there on the first step that he can snatch as you go past. Repeat a lot of times. Next time, try the treat on the next step -- from now on you can start focusing on putting tempting treats like cooked ham or chicken on the next step, then the next... the idea is to let HIM make the decision to go up after the treats, not for you to push or pull him up or force him to cross them. I'd also try never to carry him from now on -- that just gives him a signal that the stairs are scary and he always needs rescuing. So focus on the training. Same approach with a ramp. It takes patience and time but treats almost always win out eventually, especially with a cavalier. :lol: If you use a clicker you can click as a reward along with the trea, of course.
If it is a real problem, talk to a good trainer -- either have someone come work with you, or get advice when you enroll in a class.
And as noted, younger dogs and puppies are often afraid of stairs. If they dn;t live in a house with stairs, they DO need to learn them. It is one of the things people tend to try to have puppies learn when young so that they don;t grow up to be fearful. Bruce has mentioned how they give all their puppies 'star practice' while they are young and inquisitive and learn fast.