During the Zhou dynasty, 徙 was represented with the phonetic borrowing 屎 (OC *hliʔ, *hri, “excrement”), with the components 辵 and 止 later being added to differentiate the character used to represent "migration". During the Warring States period, the earlier forms of 屎 consisting of 小 or 少 components (as seen in and ) had these portions transform into 米, however 徙 continued to retain the 少 form. The Chu script form of 屎 corrupted into a form with the 尸 ("body") component becoming 尾 ("tail"), while the Qin script form of 徙 omitted the 尸 component of 屎 and left only 少 remaining. Li Shoukui (2015) however argues that the Chu script ⿸尾少 may not actually be cognate to ⿸尸少 (and ergo 屎). The clerical script form inherited the Qin script form, however had the 少 component mutate into another 止, which coincidentally resulted in the clerical form matching the same character structure as 歨 (the Shang dynasty form of 步) with an additional 彳 component.
Shuowen Jiezi erroneously takes this mutated clerical script form of 徙 with two 止 components, and claims that it is a phono-semantic compound (形聲／形声, OC *selʔ): semantic 辵(“walk”) + phonetic 止(OC *kjɯʔ). It also omits one of the 止 components to create an alternative form 𢓊, however no such character exists in ancient writing (although coincidentally it has a similar shape to the Shang and Zhou 延). Hu Houxuan (1981) states that the "ancient script" form of 徙 in Shuowen, 𡲴, comes from a corruption of the variant form featuring 尾 in place of 尸, but with the tail portion misrepresented as 火. For this reason, the "ancient script" forms of 徙 provided in Shuowen are extremely corrupted.
Li Jiahao (2010) notes that the ancient form of 屎, namely ⿸尸少, may potentially suggest that 徙 is a phono-semantic compound (形聲／形声, OC *selʔ): semantic 辵(“walk”) + abbreviated phonetic 沙(OC *sraːl, *sraːls).
↑ 1.01.11.21.31.41.5Li Shoukui (李守奎) (April 2015), ““屎”與“徙之古文”考 [On the ancient glyphs of “屎” and “徙”]”, in 出土文獻, volume 6, Tsinghua University, archived from the original on 2021-01-11, pages 154-162