Is 1 Corinthians 15:28 disregarded by trinitarians? International Standard Version:

But when everything has been put under him, then the Son himself will also become subject to the one who put everything under him, so that God may be all in all.

The New Living Translation:

Then, when all things are under his authority, the Son will put himself under God’s authority, so that God, who gave his Son authority over all things, will be utterly supreme over everything everywhere.

Jesus is made subject to God, under God's authority so he cannot be equal to God.
Please note this verse refers to a resurrected Christ.
I would like to know if the verse is disregarded by trinitarians or how they reconcile it with their beliefs.
That the Son (in regard to his Deity) should have a relationship with his Father, which is a matter of filial and voluntary subjection, does not mean that he is not equal in Deity to the Father.
Equal in Divine nature, or 'form', as we see in Philippians :

who, being in the form of God, thought it not robbery to be equal to God, [Philippians 2:6 YLT]

Yet within that equality of Deity, the Son says :

... My Father is greater than I. [John 14:28 KJV]

One needs to understand both the matter of divine nature and also the matter of divine relationship within that nature.
And one also needs to bear in mind the fact that God is God in respect of the Son of God's divine nature but also God in regard to the humanity of Jesus Christ.

But unto the Son [God saith], Thy throne, O God, is for ever and ever: a sceptre of righteousness is the sceptre of thy kingdom. [Hebrews 1:8.]

I think the premise of the question is incorrect.
Trinitarians, in general, are very well aware of the whole balance of truth in regard to both divine nature, divine relationship within that nature, and well aware of the relationship in regard to the humanity of Christ, also.
The text under discussion (1 Corinthians 15:28) is not disregarded. It is well understood.

and when the all things may be subjected to him, then the Son also himself shall be subject to Him, who did subject to him the all things, that God may be the all in all.


[1 Corinthians 15:28 Young's Literal Translation]

The question expresses an unsubstantiated opinion about the 'disregard' to the text and I do not think that opinion is correct. My experience of Trinitarian denominations over the past fifty three years of my life (I was converted at the age of sixteen in 1967) is that the text is not disregarded. It is fundamental to a proper understanding of the divine relationship of the Son of God to the Father and of the human relationship of Jesus Christ to God.

Basil the Great, 330-379, who supported the Nicene Creed, had this to say about 1 Corinthians 15:28 :

So there need be no hesitation from anyone in taking this to mean that what the Father is greater than is the form of a servant, whereas the Son is his equal in the form of God

And Augustine of Hippo, 354-430, comments thus :

when every creature is made subject to God, including even the creature in which the Son of God became the Son of man, for in this created form “the Son himself shall also be subject to the one who subjected all things to him, that God may be all in all (1 Cor. 15:28).

Both Quotes are from secundumscripturas Basil and Augustine on 1 Corinthians 15:28
Athanasius of Alexandria, 297-373, writes on the same text :

For this subjection, no more involves inferiority of essence, than His subjection (Luke 2:51) to Joseph and Mary involved inferiority of essence to them.

This quote is taken from the Cambridge Bible Commentary paragraph on Biblehub - 1 Corinthians 15:28 on which page are extensive articles by Trinitarians who quote other Trinitarians in some very involved and learned discussions, dealing with the original language in precise and academic detail.
No. Not at all 'disregarded'.