It's important to enter company port with spirit (3,4)
I believe the answer is:
con brio
'with spirit' is the definition.
(musical direction)
'it's important to enter company port' is the wordplay.
'it's important' becomes 'nb' (I can't justify this - if you can you should believe this answer much more).
'to enter' indicates putting letters inside.
'company' becomes 'co' (abbreviation).
'port' becomes 'rio' (Rio de Janeiro is a port).
'co'+'rio'='corio'
'nb' going into 'corio' is 'CON BRIO'.
Can you help me to learn more?
(Other definitions for con brio that I've seen before include "Energetically" , "Musically, with spirit" , "Lively, musically speaking" , "In music, with spirit and verve" , "In music, with verve or vivacity" .)