The line against a stock appreciation right is drawn in a regulation, and it is the whole distinction. Under 26 CFR 31.3121(v)(2)-1(b)(4)(ii), a "stock value right" is a right entitling the employee "to a payment for each share of stock equal to the excess, or a percentage of the excess, of the value of a share of the employer's stock on the date of exercise over a specified price (greater than zero)". The regulation then says outright that "the term stock value right does not include a phantom stock or other arrangement under which an employee is awarded the right to receive a fixed payment equal to the value of a specified number of shares of employer stock". Appreciation only is one instrument; full value is a different one, and the tax rules follow the difference rather than the label on the award.
That difference decides whether the arrangement is deferred compensation, and phantom stock is. The same regulation excludes stock options, stock appreciation rights and other stock value rights from the deferral rules. Phantom stock is not among them. Example 8 of the regulation works through a plan crediting an employee each year with a dollar amount equal to the value of a fixed number of shares, payable on termination. It concludes that the plan "provides for the deferral of compensation" because the employee has a legally binding right in one year to something paid in a later one, and then explains why the exclusion does not rescue it: the plan is not a stock value right "because it provides for awards equal in value to the full fair market value of a specified number of shares ... rather than the excess of that fair market value over a specified price". The timing makes it deferred compensation; the full-value design is what keeps it there. Two consequences follow.
Consequence one: section 409A applies. Payment is confined to the events that section 409A permits, deferral elections generally have to be made before the year the services are performed, and accelerating a payment is generally prohibited. The rules, the permitted payment events and the tax cost of breaking them belong to the nonqualified deferred compensation entry, which covers them in full. What matters here is the fact that they apply at all, because employees frequently assume an award described in shares is governed like equity when it is governed like a deferred bonus.
Consequence two: the Social Security and Medicare timing is not the income tax timing. Deferred compensation is subject to a special timing rule under section 3121(v)(2) of the Internal Revenue Code, which treats the amount as Social Security and Medicare wages at the later of when the services are performed or when the amount stops being subject to a substantial risk of forfeiture, rather than when it is paid. For a phantom stock award that will usually be a much earlier year than the payment. Why that timing is generally favorable, and what the accompanying nonduplication rule does, belongs to the nonqualified deferred compensation entry, which works it through. The point here is only that an employee reading the payment date as the tax date has the employment tax half wrong.
The unsecured promise is the risk, and it is not a technicality. Until the employer pays, the participant holds a contractual claim ranking with the company's other general creditors. A shareholder in the same company at least holds an asset that survives the employer's insolvency in whatever diminished form; a phantom stock participant holds a promise. Employers sometimes set money aside informally in a trust to fund these promises, but such a trust must by design leave the assets reachable by the employer's creditors, so it changes the employer's discipline rather than the employee's protection.
Valuation is the practical question at a private company. Phantom stock only means something if there is an agreed way to value a share, and in a company with no market that method is a contract term: a formula, an independent appraisal, a multiple of earnings, or a price set at a transaction. The award is worth reading for that clause before it is worth reading for the numbers.