Is this out of context..?

Usually 'utmost' rather than 'foremost' importance. Not 'upmost' which does not exist in normal British English - possibly you were thinking of 'uppermost'- certainly not usual with 'importance'. If you are not allowed to use 'utmost' then 'foremost' would be reasonable, but doesn't sound brilliant; try also 'greatest'. 'Utmost' is really the word I would use there, it is a common linking in British English.