The phrasal verb 'tear up' is separable because you can say 'She tore the letter up' or 'She tore up the letter'.
* tear up 是可以分开的短语动词，因为既可以说 She tore the letter up ，又可以说 She tore up the letter。
《牛津词典》
2
Structural analogy analogizes non-verb-object structure into a verb-object structure, when the original non-verb word group was set forth as the separable word.