You need to be able to code at least using procedural methodologies
hacking at a pre written script does not constitute the skill level of a junior developer. An employer wants the best he can get and by advertising for a junior role normally means that he is after someone with skills but maybe does not have enough work experience to make it as a professional developer. In return the employer pays less money but hopes you will bring something to the table
You will be expected to know PHP to a decent level.
A junior developer role is different from a trainee role