iPhone SE broke after only a few seconds in water

Can you prove the iPhone you purchased was new? How do you know it wasn’t previously tampered with?

New Apple iPhones purchased from Apple or an Apple Authorized Resellers come with a 1 year warranty for defects in labor or parts. However accidental damage is not covered. Apple and third party insurers sell various forms of coverage that includes accidental damage.

You are confusing a controlled laboratory test....(your numbers are not correct, but that is not really relevant here).....with accidental damage in the real world. The phone was dropped, it likely hit a hard surface before it slid into the water.

I'm sorry, but water damage is not covered under the warranty.

If it was sold on eBay, it was not "new". There are no authorized sellers of Apple products on eBay.

The water resistance statistics are based on laboratory testing under controlled circumstances. Water resistance is NOT "waterproof".

Liquid damage is not repairable.

It's toast. You may be able to get an out of warranty replacement from Apple. In the US, that will cost you $299 + tax.

You’re welcome. There are a couple more possibilities. One is a home owners policy. But the deductible may be more than the replacement cost. If you purchased it with a credit card, some cards add insurance as a benefit for being a cardholder. If you pay your cellphone bill with a credit card, some cards provide damage coverage. I got my granddaughter’s iPhone replaced that way. I pay my cellphone bill with a Wells Fargo card that offers the benefit.

Your daughter and grandson were lucky. You were not. It's entirely possible that the phone you bought had been opened, or damaged, or otherwise tampered with. Since it came from an unauthorized source and was not 'new', there's no telling what happened to it before you got hold of it.

"Water resistant" ≠ "waterproof".

It was damaged after only a few seconds because the conditions of its exposure to liquid allowed liquid to penetrate the device. How? We don't know. We are not psychic. It happens. That's exactly why it's called "water resistant" and not "waterproof".

it really was only seconds down the toilet and yet everywhere I am reading that it should be able to withstand quite a bit longer than a few seconds

Not if the phone hit the hard porcelain surface during the fall.

A fixed controlled laboratory test of resistance does not include a drop.

It didn't. It hit the water and was taken out immediately

Ah, OK. You win......but not sure how this helps you.