When you search Phonetic field data, you can combine search items with the NOT operator to narrow the search by excluding unwanted items.
NOT groups do not use any braces { } or brackets [ ], but can be used in conjunction with them.
Left side expressions:
NOT{p,b}/*_*
NOT[C]/*_*
[V]NOTp/*_*
aNOTb/#_*
NOT[[C][+labial]]/*_*
Right side expressions:
b/NOT#_*
{[C],[V]}/*_NOT<className>
{p,b}/NOT[+labial]_[+labial]
In this case, you are looking for p and b that occur after non-labial phones but before labial phones.
The NOT should be able to apply to a feature structure NOT[[C][+labial][+palatal]] or part of a feature structure [[C]NOT[+labial][+palatal]].
You may want to use parentheses to be more explicit about what the NOT is applying to as in NOT([[C][+labial][+palatal]]) or part of a feature structure [[C]NOT([+labial])[+palatal]].