Phoenix-oriented tips, then move on to more support oriented tips

I feel like I'm the only person to ever play Phoenix solo mid, but the general tips for evading stuff is the same.
Phoenix relies on his heavy nukes and his ridiculously good ult to stay alive and get kills in fights. Hence, ositioning is a very useful thing to have on him.

Phoenix should never touch the ground for more than a few seconds in fights

What I mean by that is you use your  Icarus Dive and Fire Spirits together to bombard on their faces, land, pop your laser of death for a few seconds behind the fight so you don't get stunned, move forward a little (Not too much, you still want to be behind the fight) and pop your Supernova. Once you safely respawn because you weren't stupid and popped your Supernova in the middle of the entire fight, repeat the entire process again. If the enemy is somehow not dead after all of that, chances are you've lost the fight anyways and your best choice is to run.

Those items are nice, but they are actually wastes of time on Phoenix regardless of what role you pick on him

You shouldn't need to buy a 5k Item just to stop the casual stun, because Phoenix takes a while to get the gold he needs for items and you only have 6 slots. Linkens is purchased on heroes that would be absolutely destroyed if they got initiated on and also need good stats because they lack good stat growth (Weaver, Morphling, etc)

To conclude, if you don't want to get stunned as a Phoenix, you're just going to have to position yourself better in these fights. Let the carries who are tankier and have a Black King Bar(hopefully) be in the middle of the fight.

As a side note, don't play Phoenix when you're against a Silencer. You can't juke a global silence, and his intelligence steal will punish Phoenix badly.

Supports in general

For supports in general, positioning is basically the same key component, but where to position yourself changes depending on what support you play. Rubick needs to be both in the fight and behind the fight, so he can both steal spells safely and utlise spells to their best possible use. Heroes like Keeper of the Light on the other hand should be near the back of the fight, using his Supernova abilities as well as his Q to deal lots of magical damage (and a good old mana/hp fill up as well)

If you find yourself getting stunned/silenced a lot in games, try standing back a bit more

Buying a Black King Bar only works if you've already bought all the other support items you need or you are basically the only thing capable of winning the game (Crystal Maiden  Freezing Field, Witch Doctor ultimate)

Sometimes, you actually want to be the one getting stunned

If they only have 1-2 stuns on their team, and you are the one who gets it, that means your other teammates won't get it. That includes your oh-so fragile carry or nuker in the mid game. I'm not saying go ahead and run into every stun/silence you can find, but if you're the one who gets hit by one in a fight and that's the only stun they have, you've just done your team a massive favor for a couple of crucial seconds, and sometimes seconds is all it takes for a game to be won (Million Dollar Dream Coil anyone?)