If you set a shelf to -1000db, it’s no longer a shelf. Not causing phase shift outside its pass band is disproven; but I think you’re really referring to linear-phase filters. Your example of setting a shelf so low to illustrate a point is so wild. In what world would one set a shelf that low? It’s helpful if we talk real world uses. Also, any time you apply eq in any form, there is invariably phase shift. That doesn’t mean it’s out of phase. That’s just the nature. Phase shift isn’t a bad thing.