Bird in mine inhaling iodine and phosphorus (5)
I believe the answer is:
pipit
'bird' is the definition.
(pipit is a kind of bird)
'mine inhaling iodine and phosphorus' is the wordplay.
'mine' becomes 'pit' (down the pit).
'inhaling' means one lot of letters goes inside another.
'iodine' becomes 'i' (I is the chemical symbol for iodine).
'and' means one lot of letters go next to another (I've seen this in other clues).
'phosphorus' becomes 'p' (P is the chemical symbol for phosphorus).
'i' after 'p' is 'pi'.
'pit' enclosing 'pi' is 'PIPIT'.
'in' is the link.
(Other definitions for pipit that I've seen before include "Bird related to wagtail" , "Ground-dwelling songbird" , "Meadowland bird" , "Songbird of open country" , "Lark-like songbird" .)