Tom är i våningen under.

[kirkeby]

English Translation

Tom’s downstairs.

Apparently ‘våning’ can mean both ‘floor’ and ‘apartment’ but neither word is used in the translation. It is probably better to use ‘Tom is on the floor below’ or ‘Tom is in the apartment on the floor below’.

https://en.wiktionary.org/wiki/våning#Swedish

[morbrorper]

I would say “på undervåningen”.

[kirkeby]

Yet another Swedish word we don’t have in Danish. You can say ‘underbo’ though, the person who lives in the flat below yours.