In general, text-changing effects do not modify the object's copiable values. Also in general, rules do not have a final official answer for silver-bordered cards. So if your playgroup wants to treat Phoebe as creating a text-changing effect, Spark Double will only get the rules text from the text box printed on Phoebe. (CR613.1)
Spark Double does not target anything. Its ability has you make a choice while applying the copy effect, this is not targeting.
Thanks for the quick reply! It remains tricky with silver-bordered cards indeed :).
Text-changing effects are not copied as you rightfully pointed out, but abilities that set characteristics are:
706.2. When copying an object, the copy acquires the copiable values of the original object’s characteristics and, for an object on the stack, choices made when casting or activating it (mode, targets, the value of X, whether it was kicked, how it will affect multiple targets, and so on). The "copiable values" are the values derived from the text printed on the object (that text being name, mana cost, color indicator, card type, subtype, supertype, rules text, power, toughness, and/or loyalty), as modified by other copy effects, by “as . . . enters the battlefield” and "as . . . is turned face up" abilities that set characteristics, and by abilities that caused the object to be face down. Other effects (including type-changing and text-changing effects), status, and counters are not copied.
Whether a "text box" is a characteristic is a gray area I suppose. 'Rules text' and 'abilities' count as characteristics, which would be set by the ability of Phoebe, Head of S.N.E.A.K.
An object's characteristics are name, mana cost, color, color indicator, card type, subtype, supertype, rules text, abilities, power, toughness, loyalty, defense, hand modifier, and life modifier
Or am I misinterpreting these rules? I understand that it ultimately boils down to playgroup decision, but was wondering if this reasoning is flawed or far-fetched
You've parsed that sentence in the rule incorrectly. The item in the list is "by “as . . . enters the battlefield” and "as . . . is turned face up" abilities that set characteristics," and that item doesn't apply here.
Even if there were some ability written on a card, that statically said this creature is a copy of something else, then even though Phoebe acquiring that rules text would mean it has that ability creating that effect, it still couldn't change Phoebe's copiable values because everything copiable is always finalized by the end of layer 1 of the layering system, explicitly in 613.2c. It is a change that's still invisible to Spark Double's copying.
Spark Double copying Phoebe only gets the rules text Phoebe is printed with.