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Galactic disks are highly responsive systems that often undergo externalperturbations and subsequent collisionless equilibration, predominantly viaphase-mixing. We use linear perturbation theory to study the response ofinfinite isothermal slab analogues of disks to perturbations with diversespatio-temporal characteristics. Without self-gravity of the response, thedominant Fourier modes that get excited in a disk are the bending and breathingmodes, which, due to vertical phase-mixing, trigger local phase-space spiralsthat are one- and two-armed, respectively. We demonstrate how the lateralstreaming motion of slab stars causes phase spirals to damp out over time. Theratio of the perturbation timescale ($\tau_{\mathrm{P}}$) to the local,vertical oscillation time ($\tau_z$) ultimately decides which of the two modesis excited. Faster, more impulsive ($\tau_{\mathrm{P}} < \tau_z$) and slower,more adiabatic ($\tau_{\mathrm{P}} > \tau_z$) perturbations excite strongerbreathing and bending modes, respectively, although the response to very slowperturbations is exponentially suppressed. For encounters with satellitegalaxies, this translates to more distant and more perpendicular encounterstriggering stronger bending modes. We compute the direct response of the MilkyWay disk to several of its satellite galaxies, and find that recent encounterswith all of them excite bending modes in the Solar neighborhood. The encounterwith Sagittarius triggers a response that is at least $1-2$ orders of magnitudelarger than that due to any other satellite, including the Large MagellanicCloud. We briefly discuss how ignoring the presence of a dark matter halo andthe self-gravity of the response might impact our conclusions.

A Comprehensive Perturbative Formalism for Phase-Mixing in Perturbed Disks. I. Phase spirals in an Infinite, Isothermal Slab