A method is provided for constructing upper triangular square matrices over the univariate polynomial ring over a finite field, under certain constraints on the eigenvalues of the matrices. In some cases of interest, the degree of the determinant of such matrices is shown to be the smallest possible. The method is then applied to construct generator polynomial matrices of quasi-cyclic codes for correcting phased burst errors. Finally, an interpolation-based list decoding algorithm is presented for these codes, which, for a wide range of code parameters, is shown to outperform existing list decoding schemes.