It is difficult to know what Nephi foresaw as the secret combinations. Jacob has mentioned them in his speech (2 Nephi 9:9) and they will become prominent later in the Book of Mormon, but their specific relevance to the gentile population is not clear. It is certainly an evidence of their apostasy, but there is no clear historical association. One might be tempted to see the Masons as this “secret combination” but the adoption of Masonry by Joseph and many of the brethren would argue against that conclusion.
Textual: Nephi’s language of being bound with a flaxen cord is not specifically used in Isaiah, but there is a passage where Isaiah presents the same theme:
Isa. 5:18
18 Woe unto them that draw iniquity with cords of vanity, and sin as it were with a cart rope