Does anyone know a poem that relates to anger (2nd stage of grief) in terms of loss of a loved one? Preferably one with 10-20 lines.

A lot of poetry that we see deals with deep emotions, but, surprisingly (at least to me), anger is not one of the more common emotions we find in popular poetry. So, if you want to find a poem about anger specifically related to loss, we'll have to do a little digging.
Wilfred Owen fought as a soldier in World War I and became a famous anti-war poet. The content of the poems may not be exactly what you're looking for, but you could take a look at his poems titled "Dulce Et Decorum Est" and "Anthem for Doomed Youth," as they are about his anger related to the death of his fellow soldiers in war.
You could also look at "On Pain" by Khalil Gibran, and "Eurydice" by H.D. There's also "Those Winter Sundays," by Robert Hayden, but that one's more about the poet being angry with himself for not being aware of the sacrifices his father made for him in life.