On every country having the same tax as Ireland, that is kind of what happened with the pact. Except that some countries won´t accept it, thus leaving room open.
First, there was no pact, Ireland didn't agree to it, so the rest can get that 15% and stick it where it belongs.
Second it no on every country having the same tax as Ireland but more on Ireland raising its tax to other countries levels.
On the manufacturing on poor or rich countries, that is unrelated to tax, as the price of the iPhone is unrelated to its real production cost. I am not saying that it should be manufactured in one place or another at all. The example is how the tax that should be paid in the manufacturing country and then in the destination country gets avoided by stating most of the profit as made in a third country that does nothing but has low tax.
Why should any tax be paid in the manufacturing country?
You made a product worth 25$, here is 25$, goodbye!
I bought something worth 25$, it's my business to whom I sell it and how much and where this happens, my money my product!
If I sell you my car and I make 2000$ on top of what I bought it a year ago should I pay 10% to the German government because it was manufactured there?