Inverse synthetic aperture imaging ladar (ISAL) can achieve high-resolution images, and yet it faces pulse-to-pulse high-order phase errors that the microwave radar can ignore. The high-order phase errors are almost caused by mechanical vibrations in general, which blur the azimuth focusing effect. This paper presents an ISAL imaging model to obtain high-resolution images. A novel modified cubic phase function (CPF) algorithm is proposed to compensate the additional high-order phase errors. Some high-resolution well-focused ISAL simulation images and real target images are shown to validate the methods. It is shown that the third-order phase errors are compensated by the distinctive digital signal process and the image entropy of real target images is reduced significantly.