What is the ruling on acquaintance between the sexes via phone or messaging only with the intention of marriage, with the family's knowledge, and with adherence to Sharia guidelines and without speaking in a soft or alluring manner?

The term "acquaintance" (تعارف) can be misused. If it is intended for a man to get to know a woman for the purpose of engagement, this can be done through his mahrams or her mahrams. The suitor is permitted to look at the prospective fiancée only [for this purpose], and he is not allowed to look at her after that except after the marriage contract.

However, if it is intended for going out, recreation, exchanging communications, and talking mixed with jesting and laughter, then this is Islamically forbidden, whether the woman's guardian gives permission or not, because it is a gateway for Satan.

But if the matter is restricted to a necessary communication to know something that cannot be known except from the woman herself, or for legitimate needs, and with modesty and propriety, and without seclusion (khalwa), then there is no objection to it, especially if it is via phone or messaging.