[pjc50]

Would secure-wiping the phone if involved in a legal discovery process be considered destruction of evidence?

Yes, if it's not part of a routine process.

[rhino369]

If you are already in litigation there is almost always a litigation hold, and you can't even wipe it as part of a routine process.

[dredmorbius]

However if prior to receiving notice of the hold you'd wiped it as part of a documented data retention policy, odds are far smaller of falling afoul of legal process.

Sudden change of policy in conjunction with other shady events, harder time.