What kind of literacy device is "“Amen” stuck in my throat."?

Let's understand what the first sentence means before we look at "stuck in my throat."

But wherefore could not I pronounce “Amen”?

This sentence means (in modern English):

Why couldn't I say "Amen?"

Now, let's look at the second sentence.

I had most need of blessing, and “Amen” Stuck in my throat.

The first part ("I had...blessing") of the second sentence means:

I need God to bless me...

Macbeth needed God to bless him, but "Amen" was "stuck in my [his] throat." This means that "stuck in my throat" has to be the reason that Macbeth couldn't say "Amen."

Now, we need a little bit of context from Macbeth to figure out why "Amen" is "stuck in my [his] throat."

Macbeth had killed the king, Dunkin, and felt guilty.

When I feel guilty, sometimes it feels as if my throat is closing. Shakespeare is using this feeling figuratively to explain why Macbeth couldn't say "Amen." Shakespeare's choice of "stuck in my throat" makes it sound as if Macbeth's throat was actually closing, so the word "Amen" was blocked from reaching Macbeth's mouth and couldn't be spoken.

This is an example of a metaphor (thank you, Kate Bunting, for your assistance).

Note: "Stuck in my throat" could also represent the fact that murdering Duncan was sinful, so Macbeth is separated from God and cannot receive blessings from God.