Rambly thoughts cos I've been trying to counter pharahs lately on teams which already had several bad soldiers:

Winston can hassle bad pharahs to death pretty easily, I mean half the time they hit jump-jet and ignore you, they just assume you're not a problem and chuck rockets at your teammates while you take off 75% of their health. They land, realise they should have shot the monkey, but can't pop your bubble quick enough to prevent your leap from recharging. At which point, if they've had healing, you escape, and if they haven't, they get finished off.

Thing is you aren't a threat to a decent pharah. They won't ignore you on the ground, they won't ignore the threat of you jumping with them, and they'll know that this isn't a fight winston can win with much health or any cooldowns left - so if they have one friendly to retreat to, you've probably at best just exchanged lives with the pharah.

D.Va flies up to them, bumps them immediately for melee-ish damage, and the first second or so of fire is going to take off more than half the pharah's max health. I think this is what OP meant by zoning her out of the air; you might not be killing her but you're comfortably forcing her to disengage from both you and her teammates.

D.Va, even without def matrix, can just fly in front of pharah's barrage and take them both out. Last resort and you need to react fast to really negate the whole ult, but it's usually a good trade-off!

If you meant using Winston's bubble, it stops about 4-5? regular rockets. Which is long enough to keep you alive til jump recharges, but useless vs a barrage. Melts it like it isn't there, although obviously it will make a tiny difference rather than literally none...