I can call you, Jonathan, a "servant," and that won't make you a Deacon (Servant).
Rom.16:1 doesn't, all by itself, tell us if Phoebe was a office bearer, only that she was identified with one of the churches as an agent of sorts. Again, the fact that she was a capable and reliable person in whom Paul had great confidence cannot tell us if she was a Deaconess.
The qualifications for the office of deacon are laid out in 1Tim.3:8ff. It appears to restrict the office to males. There are churches that take biblical authority seriously, who propose an alternate exegesis in 1Tim.3, in conjunction with Rom.16:1, and they believe they can defend women holding that office (which they may just term a named function, similar to the roll of the widows, 1Tim.5:9-10, thereby separating it still from a church office).
Is Phoebe a Deaconess, or is she simply a servant? If Paul (or Jesus) had meant women to serve in the government (the ministry, broadly) of his Kingdom, there was ample opportunity to demonstrate that will, both by example or a direct teaching. We have neither.
Jesus had followers of men and women (many of the latter out-spiritualizing the former), but he only chose twelve men as his disciples. Paul lists two offices (elder and deacon), and sets out the criteria for them; so where one might expect the clearest deliverance on such an official appointment for such a thing as deaconess, there is... nothing.
The ordinary offices of pastor, elder, and deacon, are devolved ministries. They begin as all compounded in Christ's supremacy. They are then separated out as offices. Such that, if there are no deacons then the senior office of elder must reabsorb those duties (reversing Act.6:2,6); they don't just disappear.
It follows (even if Scripture did not say so, which I suppose it does), that if the senior office is restricted to men, the same restriction would apply then also to the lesser office. Those of the lesser office may eventually be raised to the senior office; but this could not happen for a woman deacon who cannot be an elder (or a minister) lawfully.
When Paul is addressing the problems of church order in 1Cor., in 14:34ff he does not say any like, "Let them be content with being deaconesses, and that should be enough for them." Just this: nowhere do we find a NT teaching that clarifies or qualifies what are apparent restrictions on church office for women. A solitary appeal to an equivocal text like Rom.16:1 is a weak reed for support.
If ever there was a NT teaching involving a change like this (in terms of what was formerly limited to men in OT setting), which called for a clear reversal for a new era of operation, opening church-government to both sexes would be one. And there is none.