In the first place, you mean phonemic orthography. But I only mention that to be a jerk.
In the second place: Assuming you’re serious: do we use Received Pronunciation, General American, or Australian English as the basis for this alphabet?
In the third place, do you want to add extra letters to the alphabet (there’s not enough letters now for a one-to-one correspondence with our phonemes), use diacritics more, or subtract some phonemes?