Google translating here - is it because plumpst means "fallen" and also sounds like the sound a phone might make when falling into a canal?

Exactly

Could someone translate?

> Geplumpst

Basically means something fell or as Google Translate says "flopped" -- however, GP seems to be excited over the apparent onomatopoeia in the word because it evokes the sound of something falling in water.

> "Mir ist grad mein handy in den Landwahrkanal geplumpst"

This essentially says "My cellphone fell in the canal!" but with the delicious "geplumpst" word sound.

> "Jetzt könnte ich ein Bier gebrauchen"

This exclaims "I could use a beer now".

"geplumst" is the funny part here, it's very colloquial, kinda silly-sounding, playful – similar to "plumped". Just makes the whole sentence more delightful.

it also rhymes with "gebumst" which means "banged" or "fucked"...

"My phone just plopped into the Landwehr Canal."

"Hahaha and now what"

"Great question"

"Now I could use a beer."

I would say the best translation to English is 'plopped' - it's a sort of whimsical or even comical way of saying it fell in.

From the context and the word "Bier", "I'd like to grab a beer" perhaps

> Mir ist grad mein handy in den Landwahrkanal geplumpst

My cell phone just fell into the Landwehr Canal

> Jetzt könnte ich ein Bier gebrauchen

I could use a beer now

(Google's translations, not mine)