Hey, I play bowser a bit more than fox, but I'll just reinforce what @
Foster J.
said. Against projectile heavy chars with Bowser I run and shield until I get to a favorable distance. Most projectile spammers stay near the ledge which is a very bad idea actually. When you are just outside of their throw/jab reach (be careful of toon link's grab range), then you are at a perfect distance to respond with a grab or dash attack which fox can definitely combo off of both at low percents. Reflector is okay, but you need to be tactful with it and not rely too heavily on it. I definitely would suggest using reflector a bit more against Robin, her projectiles can be a bit more difficult to punish from just shielding. Using running shields and power shields, I usually manage to get in fairly easily with Bowser who has no reflector, so you should be fine once you figure it out.
If you notice that your opponent likes to roll into you when you get close, then just dsmash or utilt. Just be mindful of your spacing and never power shield too close to them. Mid-range going into close-range seems to be the safest option since you can punish them easier from that distance. Fox can always close in with SH nair for a mix up as well. Once you get in, stay in and never let up. Dash attack punishes rolls if timed well, which many projectile spammers will spam roll away from you once you are close. Fox is great at keeping up the pressure like this, just be patient if they get to a long range game again. Good luck!