In this paper, a novel phase-smoothing method is proposed to efficiently interpolate the fine resolution frequency data from sparse samples in the high-frequency range. This is achieved by taking the effect of the complex exponential term e−jkr in the electromagnetic field into account, which causes the oscillation in the system response especially in the high-frequency domain. By phase-smoothing, even though the magnitude of the field quantity is unchanged, both real and imaginary parts of the frequency response become smoother. The interpolation is performed separately for both real and imaginary parts so that the sample rate required for accurate reconstruction is significantly reduced. The interpolation is carried out by the matrix pencil method, the coefficients of which are calculated by using the total least squares implementation to improve accuracy. Several numerical examples are presented to illustrate the applicability of this unique phase-smoothing method in ultra-high-frequency bands.