Is it possible to invert phase by using biquad? (2nd order IIR)
Rather than swapping speaker terminals in crossover, I would prefer to do in SW.
I have found formulas for different filter types (HP, LP, All-pass, ...) but I'm not sure if it is possible to invert the phase using biquad and if so, how to calculate a and b coefficients.

Thanks

I might be missing something, but if you want the same effect as swapping speaker terminals, that's the same as multiplying by -1.   i.e., a sign inversion will do it, you don't need a filter, OR, you can invert the sign on an appropriate coefficient(s) in an existing filter.