In this talk, we consider inverse scattering with phaseless total-field data at a fixed frequency. We will propose a new framework to study this problem, including the uniqueness issue and a factorization-type imaging algorithm. Precisely, we will establish the asymptotic property in an operator norm of the phaseless total-field operator defined in terms of the phaseless total-field data measured on a large enough ball, employing the theory of oscillatory integrals. As far as we know, this is the first result on the asymptotic behavior in an operator norm of the phaseless total-field operator though pointwise asymptotic results of the phased scattered field have been previously obtained. This asymptotic property of the phaseless total-field operators is then used to establish uniqueness results and an approximate factorization method for inverse scattering with phaseless total-field data at a fixed frequency.