Tiefling Draconic sorcerer w/ Flames of Phlegethos as a tank?

[whateew]

If you really want to stretch this, I'd heartily recommend the clockwork soul sorcerer. You get the armour of agathys spell (which can be quickened, making it way more useful for a tank imo), which adds additional punishment to melee attackers.
Then, you spend your sorcery point on that ward feature the sorcerer gets, which prolongs your temporary hitpoints, allowing you to get a ton of use out of an upscaled armour of ag. Otherwise, you get a bunch of free additional spells known, who can say no to that?

If you want to really lean into this melee tank thing, consider building a sorcadin with 2 in paladin. You could use gfb to reliably power your flames, and having smites to threaten your enemies with is a great way to try and force them to fight you

You could also instead build a warlock around this I guess, going hexblade and attacking with cha, using gfb to proc flames, and pre-casting an upscaled armour of agathys. This is one of those few characters who could benefit from metamagic adept - extended spell on armour of agathys would let you short rest to recover the slot after casting twice per long rest, which might be nice. Quickened spell to rush cast it in combat too. Reading your genielock idea, that'd also be a great way of getting armour of agathys (useful spell for a tank, and fits your hit-me vibe, but perhaps I'm pushing it a bit hard here), and it wouldn't force you to be a melee fighter which is very nice (and makes a fantastic 1 level dip).

If you are a tad hexblade phobic, as I am, you can also use a celestial lock who takes shillelagh and gfb as your tome spells, or just focus dex rather than cha. Not as easy, but you get some bonus action heals to help the people you tank for, and you get a pretty potent gfb. If your DM is the type to give you a free racial feat, or would let you swap out some of your race features for said feat, that could be fun. You could get a very fitting hellish rebuke too, although I don't think it'd be a good use of slots haha

Possibly, you DM may even let you take it as a custom lineage feat for a weird "holy tiefling" flavour, renouncing their heritage by taking a pact and thus having FoP instead of the normal stuff. While not RAW allowed, most of the people I play with would allow such things (especially as this build doesn't seem too nuts compared to a PAM sentinel)

A fun build could look like:
Custom lineage with 15 +2 Dex, 15 +1 cha, flame of phlegthos.
Celestialock, taking armour of agathys as a spell and GFB as a cantrip. You take pact of the blade at 3rd to use a rapier to attack, moderately armoured at 4th to get you and off hand shield and round off your dex, and improved pact weapon.

By 6th level, you could in the right situation swing a rapier at +6 to hit, using gfb to deal (1d8 + 4 + 1) 10 magical piercing + (2d8 + 2 X cha) 15 fire damage. Not a DPS god, and it requires two closeby enemies, but it could work as well as for the sorcer. It would reliably proc your FoP as well as get you some armour of agathys usage.